The invention generally relates to using lithography techniques in fabricating various microstructures.
There is currently a strong trend toward fabricating small structures and downsizing existing structures, which is commonly referred to as microfabrication. One area in which microfabrication has had a sizeable impact is in the microelectronic area. In particular, the downsizing of microelectronic structures has generally allowed the structures to be less expensive, have higher performance, exhibit reduced power consumption, and contain more components for a given dimension relative to conventional electronic devices. Although microfabrication has been widely active in the electronics industry, it has also been applied to other applications such as biotechnology, optics, mechanical systems, sensing devices, and reactors.
Lithographic techniques are often employed in device microfabrication. See S. Wolf et al., Silicon Processing for the VLSI Era, Volume 1xe2x80x94Process Technology, (1986), pp. 407-413. Using microcircuitfabrication as an example, photoresist materials are applied to a substrate. Next, the resist layer is selectively exposed to a form of radiation. An exposure tool and mask are often used to effect the desired selective exposure. Patterns in the resist are formed when the substrate undergoes a subsequent xe2x80x9cdevelopingxe2x80x9d step. The areas of resist remaining after development protect the substrate regions which they cover. Locations from which resist has been removed can be subjected to a variety of additive (e.g., lift-off) or substractive (e.g., etching) processes that transfer the pattern onto the substrate surface.
There is a current move toward developing photolithography techniques that may allow for forming microscale devices with smaller features. Whiteside et al., Angew. Chem. Int. Ed., 1998, 37, pp. 550-575 propose various techniques. One proposed technique involves the self-assembly of monolayers. Self-assembled monolayers (SAMs) typically form spontaneously by chemisorption and self-organization of functionalized, long-chain organic molecules onto the surfaces of appropriate substrates. SAMs are usually prepared by immersing a substrate in a solution containing a ligand that is reactive toward the surface, or by exposing the substrate to a vapor of the reactive species. The self-assembly of monolayers is potentially advantageous in that ordered structures may form rapidly.
An imprint lithography process that teaches producing nanostructures with 10 nm feature sizes is proposed by Chou et al., Microelectronic Engineering, 35, (1997), pp. 237-240. In particular, Chou et al. teaches pressing a mold having nanostructures formed therein into a thin resist cast that is present on the surface of a substrate. The resist cast is designed to conform to the mold shape. The mold is then removed from the resist cast and the substrate having the resist cast present thereon is etched such that the mold pattern is transferred to the substrate.
Chou teaches using (poly)methyl methacrylate for the resist cast. The use of this material, however, may be disadvantageous in that it is potentially difficult to form some structures in varying pattern densities. Moreover, it is perceived that the etch selectivity may be potentially undesirable for common microelectronic device processing.
In view of the above, there is a need in the art for an imprint lithography process that allows for the formation of nanostructures having high resolution for a wide range of pattern densities. It would be particularly desirable if the nanostructures could be formed in a more efficient manner relative to prior art processes.
The present invention addresses the potential problems of the prior art, and in one aspect provides a method of forming a relief image in a structure that comprises a substrate and a transfer layer formed thereon. The method applies to forming structures with nanoscale patterns. The method comprises covering the transfer layer with a polymerizable fluid composition; contacting the polymerizable fluid composition with a mold having a relief structure formed therein such that the polymerizable fluid composition fills the relief structure in the mold; subjecting the polymerizable fluid composition to conditions to polymerize the polymerizable fluid composition and form a solidified polymeric material therefrom on the transfer layer; separating the mold from the solidified polymeric material such that a replica of the relief structure in the mold is formed in the solidified polymeric material; and finally subjecting the transfer layer and the solidified polymeric material to an environment that allows for the selectively etching of the transfer layer relative to the solidified polymeric material such that a relief image is formed in the transfer layer.